Second Normal Form (2NF)

Posted By on October 7, 2014

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First Normal Form (1NF)
Third Normal Form (3NF)


Second Normal Form:

Before we learn about second normal form, we need to understand the following:

Prime attribute: an attribute, which is part of prime-key, is prime attribute.

Non-prime attribute: an attribute, which is not a part of prime-key, is said to be a non-prime attribute.

Second normal form says, that every non-prime attribute should be fully functionally dependent on prime key attribute. That is, if X → A holds, then there should not be any proper subset Y of X, for that Y → A also holds.

[Image: Relation not in 2NF]
We see here in Student_Project relation that the prime key attributes are Stu_ID and Proj_ID. According to the rule, non-key attributes, i.e. Stu_Name and Proj_Name must be dependent upon both and not on any of the prime key attribute individually. But we find that Stu_Name can be identified by Stu_ID and Proj_Name can be identified by Proj_ID independently. This is called partial dependency, which is not allowed in Second Normal Form.

[Image: Relation in 2NF]
We broke the relation in two as depicted in the above picture. So there exists no partial dependency.

First Normal Form (1NF)
Third Normal Form (3NF)

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Posted by Akash Kurup

Founder and C.E.O, World4Engineers Educationist and Entrepreneur by passion. Orator and blogger by hobby